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How to Calculate Chemical Score of Protein?

Published in Protein Quality 2 mins read

The chemical score of a protein is calculated by comparing the amount of the limiting amino acid in the test protein to the amount of the same amino acid in a reference protein, such as whole-egg protein.

Here's a breakdown of how to calculate the chemical score:

Steps to Calculate Chemical Score

  1. Identify the Limiting Amino Acid: The limiting amino acid is the essential amino acid present in the lowest quantity in the test protein, relative to human needs.
  2. Determine the Amino Acid Content: Measure (in grams) the amount of the limiting amino acid in both the test protein and the reference protein (e.g., whole egg protein).
  3. Calculate the Ratio: Divide the amount of the limiting amino acid in the test protein by the amount of the same amino acid in the reference protein.
  4. Multiply by 100: Multiply the resulting ratio by 100 to express the chemical score as a percentage.

Formula for Chemical Score

The chemical score can be calculated using the following formula:

Chemical Score = (mg of limiting amino acid in test protein / mg of the same amino acid in reference protein) * 100

Example

Let's assume:

  • Test Protein: Wheat Protein
  • Reference Protein: Whole Egg Protein
  • Limiting Amino Acid in Wheat Protein: Lysine
  • Amount of Lysine in Wheat Protein: 20 mg
  • Amount of Lysine in Whole Egg Protein: 50 mg

Using the formula:

Chemical Score = (20 mg / 50 mg) * 100 = 40

Therefore, the chemical score for wheat protein, with lysine as the limiting amino acid compared to whole egg protein, is 40.

Importance of Chemical Score

The chemical score is a useful metric for evaluating the quality of a dietary protein. According to research, the chemical score is defined as the ratio of a gram of the limiting amino acid in a test diet to the same amount of the corresponding amino acid in a reference diet (eg, whole-egg protein) multiplied by 100. A higher chemical score suggests a protein source that more closely matches human amino acid requirements. This means a protein source with a higher chemical score is more efficient in supporting bodily functions.

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